Hydraulic system for limiting deflection of a piston stop

ABSTRACT

This invention relates to a hydraulic system for machine tool operation which limits deflection of a stop at the end of machine tool travel. The hydraulic system includes a cylinder, a piston, a fluid line connected to one end of the cylinder, with the fluid lines being alternately pressure and exhaust lines. Fluid under pressure is introduced alternately in one of the fluid lines for moving either a piston or a cylinder housing relative to the piston and a means for reversing fluid flow in the lines acts to move either the piston or cylinder housing back and forth. Maximum flow pressure is maintained in one of the fluid lines when used as a pressure line, and a minimum fluid pressure is maintained in one of the fluid lines when used as an exhaust line. The cylinder housing includes a stop whereby said minimum fluid pressure on one side of the piston acts against the maximum fluid pressure on the other side of the piston for limiting deflection of the stop.

United States Patent Cunningham [451 May 16, 1972 [54] HYDRAULIC SYSTEMFOR LIMITING DEFLECTION OF A PISTON STOP [72] Inventor:

[73] Assignee: I-Iardinge Brothers, Inc., Elmira, N.Y.

[22] Filed: Dec. 17, 1969 [21] App]. No.: 885,891

Henry L. Cunningham, Horseheads, N.Y.

Primary Examiner-Edgar W. Geoghegan Assistant Examiner-Irvin C. CohenAttorneyShlesinger, Arkwright & Garvey ABSTRACT This invention relatesto a hydraulic system for machine tool operation which limits deflectionof a stop at the end of machine tool travel. The hydraulic systemincludes a cylinder, a piston, a fluid line connected to one end of thecylinder, with the fluid lines being alternately pressure and exhaustlines. Fluid under pressure is introduced alternately in one of thefluid lines for moving either a piston or a cylinder housing relative tothe piston and a means for reversing fluid flow in the lines acts tomove either the piston or cylinder housing back and forth. Maximum flowpressure is maintained in one of the fluid lines when used as a pressureline, and a minimum fluid pressure is maintained in one of the fluidlines when used as an exhaust line. The cylinder housing includes a stopwhereby said minimum fluid pressure on one side of the piston actsagainst the maximum fluid pressure on the other side of the piston forlimiting deflection of the stop.

4 Claims, 1 Drawing Figure ll? 5P "919710 3 I38 I44 .IOB I220 124 ME2200 I46 2'80 Tp now? we zozf 2l4u J26 PRESSURE I28 REDUCING I32 126VALVE PITENT'Enm 1a m1 ATTORNEYS HYDRAULIC SYSTEM FOR LIMITINGDEFLECTION OF A PISTON STOP This invention relates to hydraulic systemsto be used in an automatic chucking machine" for automatic precisionfinishing of work pieces.

PRIOR ART DEVELOPMENTS Machine tools which include a hydraulicallymotivated piston device for moving a machine part into working positionare old in the art. Cunningham, U.S. Pat. No. 3,224,070, Dec. 21, 1965,discloses one of those machine tool devices. The Cunningham patent,issued to the inventor of the hereindescribed invention, generallydiscloses the basic mechanical structure, machine tool operation, andelectric circuitry used in this invention. This invention, although itcould be applied to the machine described in the Cunningham patent, isdesigned primarily for use in an automatic chucking machine.

Significant problems arise in the operation of the automatic chuckerwhen this invention is not included in the hydraulic circuitry. When thecross slide and turret carriage are moved into position by theirrespective piston devices, their pistons near the end of movement towardtheir respective work pieces, contact a solid stop. Before the presentinvention is applied to those operations, both the cross slide andturret carriage hit their respective solid stops and then very slowlycreep into final position. This consumes from two to ten secondsdepending on the rate of feed at which the controlling feed valve isset.

This time lag is caused by the mechanical deflection of the solid stopsas the pressure differential between the two sides of the pistonchanges. Upon metering the fluid exhausting from the cylinder whendistance between the piston and its stop is decreasing, pressure on theexhaust side remains slightly under pressure on the pump side until thepiston hits the solid stop. When the solid stop is contacted thepressure in the exhaust side slowly bleeds off, the length of timedepending on the feed valve setting. With pump pressure remainingconstant the pressure exerted by the piston device against the solidstop gradually increases as the exhaust side pressure is reduced,thereby slowly deflecting the solid stop and changing the position ofthe cross slide and turret carriage which, in turn, moves the machinetool. This change of position occurs until the exhaust side pressurebleeds down to atmospheric pressure at which time the movement ceases.

The above-described situation makes it difficult to machine close-turneddiameters and bores on work pieces without a relatively long time delayto allow the machine tool to settle into its final position against thestop. That time delay considerably lengthens the cycle time of anautomatic machine tool mechanism.

Additionally, when the four-way valve controlling fluid movement shiftsto reverse the direction in which the cross slide or turret carriagemoves, the cross slide or turret carriage takes a momentary jump causedby the stop moving back to its pre-deflection position. If the tool isin contact with the work piece, a mark is cut into the work piece, whichis in many cases objectionable. This jump is caused by no pressure beingpresent in the exhaust side of the cylinder through the fourway valvebetween the cylinder and the choke valve.

The subject matter of this invention discloses a workable solution tothe hereinbefore described problems.

OBJECTS AND SUMMARY it is therefore, an object of this invention toprovide a hydraulic system for machine tool operation which reduces thetime that it takes for a carriage and cross slide of a machine such asan automatic chucker to move into final working position.

Another object of this invention is to provide a hydraulic system formachine tool operation which reduces the cycle time of an automaticchucker.

Still a further object of this invention is to provide a hydraulicsystem for machine tool operation which considerably reduces the timerequired by a machine tool slide to creep into a final accurateposition.

A further object of this invention is to provide a hydraulic system formachine tool operation which creates a condition in the exhaust side ofa piston so the fluid pressure on the exhaust side will not have tobleed down to atmospheric pressure for piston controlled slides to reacha final accurate position.

Still another object of this invention is to provide a hydraulic systemfor machine tool operation which maintains an adjustable constantminimum hydraulic pressure in fluid exhaust lines.

Yet a further object of this invention is to provide a hydraulic systemfor machine tool operation which limits mechanical deflection of a solidstop once it is contacted by a piston device moved under relatively highpressure.

Still a further object of this invention is to provide a hydraulicsystem for machine tool operation which utilizes a pressure reducingvalve to maintain an adjustable constant minimum pressure in fluidexhaust lines.

Yet another object of this invention is to provide a hydraulic systemfor machine tool operation which prevents the momentary jump of amachine tool caused by the stop jumping back to its pre-deflectionposition when pressure exerted by a piston device against the stop isrelieved.

To summarize, it is therefore an object of this invention to provide ahydraulic system for machine tool operation which provides a pressuredifferential between the pump side and the v exhaust side of a pistonwhich moves a cross slide or turret carriage, the pressure differentialbeing great enough to allow the piston to move a machine tool intoworking position and small enough to prevent excessive deflection of asolid stop when contacted by the piston under pressure.

These and other objects of this invention and advantages andcapabilities will be apparent from the following description andappended claims and accompanying drawings in which:

The FIGURE is a simplified hydraulic diagram typical for use in theoperational control of the herein-described invention.

THE FIGURE The invention hereinafter described specifically relates to ahydraulic control circuit for operation of a turret carriage and crossslide for an automatic chucker, but may be adapted for use in othergenerally similar machines.

The condition of the machine parts and their working mechanisms shown inthe FIGURE is that the turret carriage and cross slide are in theirnon-working or back positions. The turret carriage and the cross slideare both retracted away from the work piece. All of the hydraulic valvesare in positions that they assume when their solenoids are de-energized,the valves being returned to this position by return springs.Altemately, the hydraulic valves, instead of being returned to theirback positions by return springs, could include another solenoid thatwould control the valves by being alternately energized and de-energizedwith respect to the first solenoid.

Hydraulic pump A, having been energized by 'a hydraulic pump motor (notshown), delivers hydraulic fluid under pressure to to pressure line 100.To maintain the turret carriage TC in its retracted position, fluidflows through line 100, through control valve 102 in its de-energizedstate, and into line 104. Fluid flows from line 104, through fluidpassage 106, and into cylinders which are connected by the cylinder port108. Piston rods 107 extend from both sides of pistons TP so thatpistons TP will be of equal areas on both sides.

As pistons TP move turret carriage TC to the right in the FIGURE toreach the position shown, fluid in cylinders 110 on the left side ofpistons TP in the FIGURE, connected by port 112, exhausts through fluidpassage 114 into line 116. As the exhaust fluid from line 116 flowsthrough control valve 102 in its position shown in the FIGURE, theexhaust fluid enters line 118. A two-way valve 122, shown in the FIGUREin its fluidpassing position, is connected by line 120 to line 118. Whentwo-way valve 122 is in its fluid-passing position, the exhaust fluidfrom line 118 flows through line 120, through two-way valve 122, throughline 124, and into sump 126. When twoway valve 122 is in itsfluid-blocking position, exhaust fluid in line 118 flows to a pluralityof solenoid-operated two-way valves, as described in detail in thehereinbefore mentioned Cunningham patent, for controlling the feed ratesfor each turret position.

Pressure reducing valve 128 is connected on one side to line 100 by line130, and is connected on the other side to line 118 by line 132. A checkvalve 134 is positioned on line 132 to prevent fluid flow from line 118into line 132 when fluid pressure in line 118 is greater than fluidpressure in line 132, while allowing fluid to flow from line 132 intoline 118 when fluid flowing in line 132 is under greater pressure thanfluid flowing from line 118. The positioning of pressure reducing valve128 as just described allows a minimum fluid pressure to be maintainedin line 116 when four-way control valve 102 is in the position shown inthe FIGURE. When four-way control valve 102 is energized line 1 16becomes a pressure line and line 104 becomes an exhaust line resultingin pressure reducing valve 128, through line 118a, maintaining a minimumfluid pressure in line 104. Check valve 134a performs the same functionas described for check valve 134 except with respect to line 1 18a.

When four-way control valve 102 is energized, it changes its positionand fluid flows through line 110 and into line 116. The fluid then flowsthrough fluid passage 114 and into cylinders 110 on the left side ofpistons TP in the FIGURE, cylinders 110 being connected by port 112,thereby resulting in pistons TP moving turret carriage TC to the left inthe FIGURE. Fluid is discharged from cylinders 110 on the right side ofpistons T? in the FIGURE, connected by port 108, through fluid passage106, through line 104, through four-way control valve 102, and into line118a. Two-way valve 122a is l the counterpart of two-way valve 122 andwhen in its fluid passing position, as shown in the FIGURE, it allowsexhaust fluid in line 118a to flow intosump 126. However, when twowayvalve 122a is in its fluid-blocking position, exhaust fluid flowingthrough line 118a is diverted to line 138. Line 138 is connected to aplurality of solenoid-operated two-way valves, as described in theCunningham patent in detail,'for controlling the feed rates for eachturret position.

As fluid under pressure enters cylinders 110 on the left side of pistonsTP in the FIGURE, pistons TP cause turret carriage TC to move to theleft in the FIGURE. When turret carriage TC reaches the end of itstravel, pistons TP contact solid stops 109 which are the end ofcylinders 1 10, but may be recognized devices such as protuberancesextending into the path of piston travel. As pistons TP contact theright end of cylinders 110, the relatively high pressure exerted byhydraulic fluid on pistons TP normally causes the solid stops 109 todeflect slightly. The minimum fluid pressure maintained in exhaust line104 by pressure reducing valve 128 limits considerably deflection of thesolid stops 109 by creating a pressure differential high enough to moveturret carriage TC to the left in the FIGURE, but low enough to preventexcessive deflection of the solid stops 109.

With the preceding description being limited to movement of the turretcarriage TC, the following will describe the operation of cross slide200. The hydraulic configuration shown in the FIGURE shows piston 201 inits back position with the cross slide 200 away from the work piece (notshown). Piston rod 205 extends on both sides of piston 201 so that bothsides of piston 201 are of equal area. The automatic chucker (not shown)is arranged so that the cross-slide 200 can be fed against stop 207while the tool is facing a shoulder on the work piece, after which thecarriage slide moves the tool axially to either turn a close diameter orbore a close hole. If this invention is not incorporated into thehydraulic circuitry for the automatic chucker and the time-consumingbleeding of exhaust pressure down to atmospheric pressure is present,the longitudinal slide would be moved before the cross slide settlesinto its final accurate work position, producing a tapered diameter orbore.

To maintain piston 201 in the position shown, fluid under pressure frompump A flows through line 202, through fourway control valve 203 in itsde-energized position, through line 204, and into cross slide cylinder206. Fluid exhausted from cylinder 206 on the right side of piston 20]in the FIGURE flows through line 208, through four-way control valve203, and into line 210. Two choke valves 212, 214 are arranged inparallel on line 210 and the flow of exhaust fluid to one or the otherof choke valves 212, 214 is controlled by two-way valves 216 and 218,respectively. When two-way valve 216 is in a fluid-blocking position,two-way valve 218 is in a fluid-passing position thereby allowing theexhaust fluid to flow through choke valve 214 and into sump 126., Whentwoway valves 216 and 218 are reversed, the exhaust fluid flows fromline 210, through choke valve 212, and into sump 126. The selectivelyrestricted passing positions of choke valves 212 and 214 act to controlmovement speed of the cross slide 200.

When solenoid 219 is energized, four-way control valve 203 shifts itsposition for moving the cross slide into working position. When theposition of four-way control valve 203 is thus changed, fluid underpressure from line 202 flows through control valve 203, through line208, and into cylinder 206 on the right side of piston 201 as shown inthe FIGURE, thereby moving cross slide 200 to the right in the FIGURE.As piston 201 moves to the right in the FIGURE, fluid from cylinder 206is exhausted into line 204, through control valve 203, through line210a, and selectively through two-way valve 216a and choke valve 212a orthrough two-way valve 218a and choke valve 214a, depending on thepositions of two-way valves 216a and 218a.

Similar to the hydraulic configuration described for the turretcharriage TC, pressure reducing valve 128 connects to lines 210 and 2100through lines 220 and 220a, respectively. Check valves 222 and 2220 arepositioned on lines 220 and 220a, respectively, to prevent fluid flowfrom lines 210 and 210a, respectively, into lines 220 and 220a,respectively, when fluid pressure in lines 210 and 210a respectively, isgreater than fluid pressure in lines 220 and 220a, respectively, whileallowing fluid to flow from lines 220 and 220a, respectively, into lines210 and 210a, respectively, when fluid flowing in lines 220 and 220a,respectively, is under greater pressure than fluid flowing in lines 210and 210a, respectively. As hereinbefore described for the turretcarriage TC, pressure reducing valve 128 maintains a minimum fluidpressure at all times in line 204 or line 208, whichever is acting as anexhaust line, depending on the position of four-way control valve 203.

Similar to the situation described with respect to the turret carriageTC, as cross slide piston 201 reaches the end of its travel in cylinder206, piston 201 comes in contact with a solid stop 207. That stop 207can either be an end of cylinder 206 in the FIGURE or a protuberanceextending into the path of piston travel. As piston 201 contacts theleft end of cylinder 206, the relatively high pressure exerted byhydraulic fluid on piston 201 normally causes the solid stop 207 todeflect slightly. The minimum fluid pressure maintained in exhaust line204 by pressure reducing valve 128 limits deflection of the solid stop207 by creating a pressure differential high enoughto move cross slideto the right in the FIGURE, but low enough to prevent excessivedeflection of the solid stop 207.

Cam switches (not shown) similar to the ones disclosed in the Cunninghampatent, control the position of four-way control valve 203 byselectively energizing and de-energizing solenoid 219.

OPERATION For an automatic chucker, the hydraulic system describedherein best operates when the fluid from pump A is introduced into thehydraulic system at approximately 300 p.s.i., and pressure reducingvalve 128 is set at 175 p.s.i. A differential pressure of approximately125 p.s.i. has been found adequate in most instances providing a minimumpressure substantially above atmospheric pressure, but this will ofcourse vary somewhat depending upon the job to be accomplished and thetype of machine used. The minimum pressure above atmospheric pressure inexhaust lines is significent in that when a piston contacts itsrespective solid stop the pressure on the exhaust side of the pistonwill only have to bleed down to 175 p.s.i. before the check valve willopen allowing the 175 p.s.i. from the pressure reducing valve to enterthe exhaust line. With the pressure against the opposite side of thepiston being 300 p.s.i., the carriage is held against the solid stop bythe pressure differential of 125 p.s.i. in a satisfactory manner. Thetime for the pressure on the exhaust side of the piston to bleed to 175p.s.i. is relatively small at any feed valve setting and the carriagequickly reaches its final accurate position with a minimum creepagecaused by deflection of the solid stop. Until pressure in the exhaustline drops to 175 p.s.i. the check valve keeps the higher pressure fromflowing back through the pressure reducing valve.

While this invention has been described in connection with the preferredembodiment, it will be understood that this invention is capable offurther modification. This application is intended to cover anyvariations, uses, or adaptations of the invention following, as well asthe principles of the invention in general including such departuresfrom the present disclosure as come within known or customary practicein the art to which the invention pertains and further including suchdepartures as may be applied to the essential features hereinbefore setforth and fall within the scope of the invention or the limits of theappended claims.

Having thus described my invention, What I claim is:

1. A hydraulic system for precision machine tool operation for limitingdeflection of a stop means at the end of machine tool travel comprising:

a. piston and cylinder means,

b. a first fluid line connected near one end of said cylinder means,

c. a second fluid line connected to the other end of said cylindermeans,

d. said fluid lines being alternately pressure and exhaust lines,

e. valve means for reversing fluid flow in said fluid lines for movingsaid piston means back and forth relative to said cylinder means,

f. a pressure reducing valve,

g. means for introducing fluid into said first fluid line and saidpressure reducing valve at a first predetermined pressure,

b. means for conveying fluid at a second predetermined pressure lowerthan said first predetermined pressure and substantially aboveatmospheric pressure from said pressure reducing valve to said valvemeans and said second fluid line, and

i. said conveying means including check valve means permitting fluidpassage from said pressure reducing valve to said valve means andpreventing fluid passage from said valve means to said pressure reducingvalve.

2. A hydraulic system as in claim 1 and wherein:

a. said valve means includes a four-way valve means, and

b. means for positioning said four-way valve means.

3. A hydraulic system as in claim 2 and including:

a. a plurality of choke valve means,

b. each of said choke valve means including a choke valve and a two-wayvalve having fluid blocking and fluid passing positions and being influid commumication with said choke valve,

c. means for selectively positioning said two-way valves, and d. a sumpconnected to said choke valves.

4. A hydraulic system for precision machine tool operation for limitingdeflection of a stop means at the end of machine tool travel comprising:

a. piston and cylinder means,

b. a first fluid line connected near one end of said cylinder means,

c. a second fluid line connected to the other end of said cylindermeans,

d. said fluid lines being alternately pressure and exhaust lines,

e. valve means for reversing fluid flow in said fluid lines for movingsaid piston means back and forth relative to said cylinder means,

f. a pressure reducing valve,

g. means for introducing fluid into said first fluid line and saidpressure reducing valve at a first predetermined pres sure,

h. means for conveying fluid at a second predetermined pressure lowerthan said first predetermined pressure and substantially aboveatmospheric pressure from said pressure reducing valve to said valvemeans and said second fluid line,

i. said conveying means including first and second check valves forreceiving fluid from said pressure reducing valve,

j. said first check valve being in fluid communication through saidvalve means with one of said fluid lines and said second check valvebeing in fluid communication through said valve means with the other ofsaid fluid lines, and

k. said check valves preventing fluid flow from said valve means to saidpressure reducing valve.

1. A hydraulic system for precision machine tool operation for limitingdeflection of a stop means at the end of machine tool travel comprising:a. piston and cylinder means, b. a first fluid line connected near oneend of said cylinder means, c. a second fluid line connected to theother end of said cylinder means, d. said fluid lines being alternatelypressure and exhaust lines, e. valve means for reversing fluid flow insaid fluid lines for moving said piston means back and forth relative tosaid cylinder means, f. a pressure reducing valve, g. means forintroducing fluid into said first fluid line and said pressure reducingvalve at a first predetermined pressure, h. means for conveying fluid ata second predetermined pressure lower than said first predeterminedpressure and substantially above atmospheric pressure from said pressurereducing valve to said valve means and said second fluid line, and i.said conveying means including check valve means permitting fluidpassage from said pressure reducing valve to said valve means andpreventing fluid passage from said valve means to said pressure reducingvalve.
 2. A hydraulic system as in claim 1 and wherein: a. said valvemeans includes a four-way valve means, and b. means for positioning saidfour-way valve means.
 3. A hydraulic system as in claim 2 and including:a. a plurality of choke valve means, b. each of said choke valve meansincluding a choke valve and a two-way valve having fluid blocking andfluid passing positions and being in fluid commumication with said chokevalve, c. means for selectively positioning said two-way valves, and d.a sump connected to said choke valves.
 4. A hydraulic system forprecision machine tool operation for limiting deflection of a stop meansat the end of machine tool travel comprising: a. piston and cylindermeans, b. a first fluid line connected near one end of said cylindermeans, c. a second fluid line connected to the other end of saidcylinder means, d. said fluid lines being alternately pressure andexhaust lines, e. valve means for reversing fluid flow in said fluidlines for moving said piston means back and forth relative to saidcylinder means, f. a pressure reducing valve, g. means for introducingfluid into said first fluid line and said pressure reducing valve at afirst predetermined pressure, h. means for conveying fluid at a secondpredetermined pressure lower than said first predetermined pressure andsubstantially above atmospheric pressure from said pressure reducingvalve to said valve means and said second fluid line, i. said conveyingmeans including first and second check valves for receiving fluid fromsaid pressure reducing valve, j. said first check valve being in fluidcommunication through said valve means with one of said fluid lines andsaid second check valve being in fluid communication through said valvemeans with the other of said fluid lines, and k. said check valvespreventing fluid flow from said valve means to said pressure reducingvalve.